One of the startups that pitched the crowd last week at The Next Web conference in Amsterdam, and whose co-founder Rahul Vohra myself and the other jury members crowned the best presenter of the bunch, was Rapportive, which loftily promises to “make email a better place”.

I promised myself to check out their product extensively over the weekend, and now that I did I’m seriously glad to have discovered them as their free software has already made my Gmail experience much better.

Rapportive is like Xobni for Gmail. It is a browser plugin for Chrome and Firefox that automatically adds a dynamic widget in the form a sidebar to incoming Gmail messages. Thanks to the extension, you’ll get a much better overview of who’s sending you emails, as the name and email address of the people who do will be automatically cross-checked for publicly available social network presences, pictures and more on the Web, all of which get displayed alongside messages.

The sidebar replaces Google’s contextual ads, so that’s a double win, unless you can’t live without advertisements in your Gmail – or if you’re Google.

As you can see in the screenshot below, Vohra recently got an email from Spark Capital’s Bijan Sabet and can immediately see what the man looks like in real life, in combination with links to his Twitter, Flickr, Facebook, MySpace, LinkedIn and other social network profiles. At the bottom, he can add a note about Sabet, turning the extension into a basic CRM tool as he’ll see those private notes every time he gets an email from him in the future.

Last week, the startup opened up to developers who would like to enhance the sidebar even more. Dubbed Raplets, these extra extensions effectively turn Gmail into a platform, enabling third parties to plug in free or paid CRM tools, social media monitoring applications, accounting software programs and more. One integration that is already in place is with our own CrunchBase, making it easier and faster to look up information about people and companies who can be found in the online database, which is growing quickly.

The startup promises to expand its service to other email platforms in the near future. Even if it’s only half as good as the plugin for Gmail, you’ll want to install it straight away.

Definitely a keeper.

For alternatives, check out Etacts and the more business-focused Appirio.